dplyr and ggplot in a function: use reorder in aes function - r

Question

I'm struggling to reorder my data for plotting with ggplot in a function that also uses dplyr:
# example data
library(ggplot2)
library(dplyr)
dat <- data.frame(a = c(rep("l", 10), rep("m", 5), rep("o", 15)),
b = sample(100, 30),
c= c(rep("q", 10), rep("r", 5), rep("s", 15)))
Here are my steps outside of a function:
# set a variable
colm <- "a"
# make a table
dat1 <- dat %>%
group_by_(colm) %>%
tally(sort = TRUE)
# put in order and plot
ggplot(dat2, aes(x = reorder(a, n), y = n)) +
geom_bar(stat = "identity")
But when I try to make that into a function, I can't seem to use reorder:
f <- function(the_data, the_column){
dat %>% group_by_(the_column) %>%
tally(sort = TRUE) %>%
ggplot(aes_string(x = reorder(the_column, 'n'), y = 'n')) +
geom_bar(stat = "identity")
}
f(dat, "a")
Warning message:
In mean.default(X[[i]], ...) :
argument is not numeric or logical: returning NA
The function will work without reorder:
f <- function(the_data, the_column){
dat %>% group_by_(the_column) %>%
tally(sort = TRUE) %>%
ggplot(aes_string(x = the_column, y = 'n')) +
geom_bar(stat = "identity")
}
f(dat, "a")
And I can get what I want without dplyr, but I'd prefer to use dplyr because it's more efficient in my actual use case:
# without dplyr
ff = function(the_data, the_column) {
data.frame(table(the_data[the_column])) %>%
ggplot(aes(x = reorder(Var1, Freq), y = Freq)) +
geom_bar(stat = "identity") +
ylab("n") +
xlab(the_column)
}
ff(dat, "a")
I see that others have struggled with this (1, 2), but it seems there must be a more efficient dplyr/pipe idiom for this reordering-in-a-function task.

Answer 1

If you are going to use aes_string, then the whole value must be a string, not just partially a string. You can use paste() to help build the expression you want to use for x. For example
f <- function(the_data, the_column){
dat %>% group_by_(the_column) %>%
tally(sort = TRUE) %>%
ggplot(aes_string(x = paste0("reorder(",the_column,", n)"), y = 'n')) +
geom_bar(stat = "identity")
}
Or you could use expressions rather than strings
f <- function(the_data, the_column){
dat %>% group_by_(the_column) %>%
tally(sort = TRUE) %>%
ggplot(aes_q(x = substitute(reorder(x, n),list(x=as.name(the_column))), y = quote(n))) +
geom_bar(stat = "identity")
}
but the general idea is that you need to be careful when mixing strings and raw language elements (like names or expressions).